I watch a lot of inspiration videos from TED (www.ted.com.au) on my new Galaxy S2 phone. However, I only do this when I am at home and can access my home wifi network.

My home wifi and the phone's 3G networks are with different providers. Obviously, my phone switches to the home wifi network automatically when I am at home.

My question: Is it possible for my 3G network provider to see/track my wifi usage and bill me accordingly (as if I am using the 3G network) because everything goes through the phone that is on their network?

I am new to smart phones so please bear with me. My monthly 3G data download allowance is only 150 MB but my home wifi came with 5 GB.

On Android, Wi-Fi is always used in preference to mobile data when connected to a Wi-Fi network.

This was quite clear in Gingerbread and older versions of Android, which removed the mobile data icon from the status bar when Wi-Fi was in use. From Honeycomb onward, the mobile data icon may remain on screen when Wi-Fi is active.

If your carrier/handset manufacturer hasn't customized the firmware too much, then (on ICS and later) the active data network will be blue, while the inactive data network will be white. (I don't have one handy, but I believe on the S2 they always appear in white, which is confusing. Still, Wi-Fi overrides mobile data.)

See this question for someone else with a similar concern. He also has a Galaxy...

To be sure you are using only WiFi connection, you should specifically turn off the mobile data connection (in that case you will have no connection if you lose the WiFi connection, instead of switching automatically to mobile data connection without you noticing.)

This was news to me! I'm surprised, since none of my older phones (Nokia S40/S60) allowed this. However, I stand by my downvote, as the OP will be unable to make or receive phone calls while in flight mode.
–
Chinmay KanchiOct 4 '12 at 14:46

As @ChinmayKanchi also noted, you will be unable to make or receive phone calls while in flight mode. This is a big disadvantage as normally this is the primary usage for a mobile phone...
–
aweMay 15 '13 at 11:52